A drive-by-wire (DBW) throttle system is an automobile technology which severs the mechanical link between the accelerator pedal and the throttle. In place of the mechanical link, an electrical connection is provided. A typical DBW throttle system includes an accelerator pedal module, an electronic control unit (ECU), and an electronically controlled throttle module.
The accelerator pedal module serves as the driver's throttle control, where the driver depresses the pedal to signal a desired increase in power. An accelerator pedal is rotatably mounted along the driver's side floor and is movable from a starting position to an end position along an arc. The pedal being pushed towards the front of the vehicle (depressed), signals a desired increase in power by the driver.
The pedal position along the arc is translated into an electrical signal. The electrical signal is sent to the ECU, where the signal is received and used to calculate the optimum throttle plate opening. This calculation is made considering the parameters acting on the system, such as vehicle speed, wheel slip, and automatic transmission shifting status. The ECU instructs the electronically controlled throttle module, which opens the throttle plate as instructed.
One benefit of the DBW throttle system is that, by electronically controlling the throttle, the integration of additional features to the vehicle is simplified. These additional features include cruise control, stability control and others that require torque (throttle) management. The integration of these particular features is facilitated because the throttle in a DBW throttle system can be moved irrespective of the position of the accelerator pedal.
Early DBW throttle systems were criticized for overruling driver decisions, however modern applications focus on making the vehicle power-train characteristics seamlessly consistent. Several of the improvements relating to the DBW throttle systems are directed to giving the driver a more natural driving feel.
One such improvement is directed to the situation where a pedal depression requires a substantial increase in power and therefore triggers an automatic transmission to downshift or “kickdown”. Advances in DBW systems relate to giving the driver a feel for when a kick-down is going to occur. In this regard, devices known as kick-down mechanisms have been installed in DBW throttle systems as a means of providing a force feedback prior to a kick-down and thereby notifying a driver of a pending kick-down.
In addition to providing a more natural driving feel for a driver, a kick-down mechanism provides other benefits. The force feedback provided prior to a kick-down allows the driver to decide whether or not to continue to depress the pedal and trigger the kick-down or down shift. Avoiding a kick-down allows the transmission to maintain a higher gear ratio for a longer period of time, providing fuel economy benefits.
A conventional kick-down mechanism uses a kick-down detent situated in a position near the end of pedal travel. The kick-down is fixed at this position and, once contacted by the accelerator pedal, requires the driver to exert an additional force to overcome the detent. The additional force provides the driver with the force feedback which serves as notice to the driver that the automatic transmission is about to perform a downshift.
A problem exists with conventional kick-down mechanisms in that the kick-down detent is in a fixed position. As road and driving conditions vary, the pedal position at which a kick-down occurs will change. While the end position of pedal travel can be a good estimation of a kick-down pedal position, conventional kick-down mechanisms fail to provide the driver with a kick-down feel when the kick-down occurs prior to the end pedal position, such as may occur at lower speeds. Therefore a need exists for a kick-down mechanism which accurately provides the driver with a kick-down feel regardless of the pedal position at which the kick-down occurs.